Start: You'll need something thick and sturdy to stand on; a 25-pound weight plate, an aerobics step, or a phone book. Put an ankle strap around one ankle and attach it to the low pulley Stand facing the weight stack, about a foot in front of it, with your nonworking foot on the weight plate. Lean forward about 45 degrees from the hips, and rest your hand on something for balance. Pull in your gut.
Finish: Pull your working leg back as far as you can without changing the angle of your torso or bending your knee. Pause, then slowly return to the starting position. Finish the set with that leg, then repeat with the other.